tree 6f464a46b5d9a0bf2c890107b1a4453a6473496f
parent 1e3b4f740717a9d6f0de39de90cedc6deb4e7255
author David 'Digit' Turner <digit@google.com> 1616497146 +0100
committer Commit Bot <commit-bot@chromium.org> 1637609683 +0000

[target] Turn many Target::foo_ fields into std::unique_ptr<Foo> ones.

There is only one Target class in GN that has accreted over time
many fields that are only used in a small number of cases. However,
many of them are quite large and complex.

Due to this, the Target::~Target() destructor appears high in profiling
traces, and heap usage is dominated by Target allocation. This CL tries
to reduce the problem by making most of these target-type specific
fields into std::unique_ptr<Foo> members instead.

The actual values are created on demand, with static constant globals
used for defaults for targets that don't need them.

Measurements with an optimized GN build and the Fuchsia source tree
show a reduction of about 200 MiB (5% of 3.8 GiB) in peak RAM usage,
and a reduction of about half a second in "gn gen" time.

For the Chromium build, there is no noticeable difference on either
metrics.

+ Refactor SwiftValues::OnTargetResolved() slightly to avoid
  creating un-needed SwiftValues instances when not needed
  (i.e. for most targets).

+ Create Target::GeneratedFile structure type to hold all
  fields related to generated_file() targets as well.

Measurements:

        FUCHSIA BEFORE

        Done. Made 173241 targets from 5370 files in 17633ms
        Done. Made 173241 targets from 5370 files in 17687ms
        Done. Made 173241 targets from 5370 files in 17691ms
        Done. Made 173241 targets from 5370 files in 17730ms
        Done. Made 173241 targets from 5370 files in 17761ms *
        Done. Made 173241 targets from 5370 files in 18130ms
        Done. Made 173241 targets from 5370 files in 18306ms
        Done. Made 173241 targets from 5370 files in 19193ms
        Done. Made 173241 targets from 5370 files in 19232ms

        3787204
        3799056 *
        3803784

        FUCHSIA AFTER

        Done. Made 173241 targets from 5370 files in 16473ms
        Done. Made 173241 targets from 5370 files in 16529ms
        Done. Made 173241 targets from 5370 files in 16717ms
        Done. Made 173241 targets from 5370 files in 16859ms
        Done. Made 173241 targets from 5370 files in 17014ms *
        Done. Made 173241 targets from 5370 files in 17192ms
        Done. Made 173241 targets from 5370 files in 17543ms
        Done. Made 173241 targets from 5370 files in 17538ms
        Done. Made 173241 targets from 5370 files in 17946ms

        3600740
        3609616 *
        3616088

Change-Id: Iedc65a3250cf73b82ae0b5d1480c32db9fd507bb
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/12401
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: David Turner <digit@google.com>